Silver halide print-out emulsions combining cadmium iodide



Nov. 5, 1963 'r. A. scoTT SILVER HALIDE PRINT-OUT EMULSIONS COMBINING CADMIUM IODIDE Filegl May 26, 1958 SILVER HALIDE MIXTURE CADMIUM IODIDE PREPARE HOMOG ENEOUS MIXTU RE AND DISP ERSE IN ORGANIC COLLOID DISPERSDN INCLUDING SILVER HALIDE AND CADMIUM IODIDE SUPPORT IN V EN TOR. TROY A. SCOT T ATTOHVEY in-tensity radiation.

United States Patent 3,l l9,737 SILVER HALE)? FRlNT-UT EMULSIGNS COMBINING CADMEUM IGDIDE Troy A. Scott, Edina, Minn, assignor to Minneapolis- Honeyweil Regulator Company, Minneapolis, Mium, a corporation of Delaware Filed May 26, 1953, tier. No. 737,758 6 Claims. (Cl. 96-168) The present invention relates broadly to photographic sensitive compositions and more particularly to photographic compositions of the printout type. The term print-out" refers to that type of photosensitive substance upon which a visible image is obtained after an initial eX- posure to light or electromagnetic radiation has been utilized to form a latent image, the visible image being obtained initially or simply by an additional exposure to such radiation. This additional exposure is known as latensification and is general in its application, including exposing the area upon which the initial image was formed as Well as the surrounding background area to an added amount of radiation. Print-out emulsion or dispersions are distinguished from development emulsions which require a development treatment such as a chemical development after initial exposure to produce a visible image, inasmuch as this image is produced by an additional exposure in print-out emulsions. The specific print-out papers coated with a film, comprising a dispersion or emulsion of the compositions of the present invention are particularly sensitive to a high intensity beam of light or other electromagnetic energy of either visible or invisible wavelength radiated across a portion of the area of the film. While the material of the present invention is particularly sensitive to such exposure, the background or non-exposed area is sufficiently stable to render a highly contrasting image upon subsequent latensification.

According to the present invention, a photosensitive silver halide is used as the basic sensitive ingredient of the composition, and a quantity of cadmium iodide is added to the silver halide in order to improve the photo response thereof. The cadmium iodide sensitizes the silver halide parti ularly to brief exposures, in the range of microseconds, from a high intensity source, but causes very little sensitization of composition to relatively lower A high degree of sensitivity to the trace coupled with a highly stable background produces a maximum contrast between the image and the background when applied to recording operations. The present invention provides this desirable combination of high image sensitivity and high degree of background stability.

The intensity of the radiation source utilized in latensification is not as critical with the sensitive mixtures of the present invention as it is with available compositions of the prior art. in other words, the accumulated quantity or intensity of illumination or radiation to which the sensitized paper is exposed during latensification is not particularly critical. The latensification rate obtainable by an intense exposure to ordinary fluorescent lamp lighting conditions has been found to be satisfactory for the silver halide compositions of the present invention, while this intensity of light is generally too great for available emulsions produced prior to the present invention.

The term halide as used throughout the specification is intended to encompass bromides, chlorides and iodides, fluorides being specifically excluded. Accordingly various silver halides may be employed, silver halides consisting mainly of or entirely of silver bromide being generally referred.

in the early development of photography, print-out papers were relatively widely used for ordinary photographic purposes. With the advent of the improved development emulsions, print-out emulsions fell into a more and more limited use and this situation continued until only recently when it was recognized that they possessed desirable properties for high speed recording such as osciliographic recording and the like. As an example, such a recording system is disclosed in the copending application of Mahoney et al., Serial No. 63 8,729, filed February 7, 1957, and entitled Recording Apparatus. Unfortunately, the sensitive papersand sensitive coating substances of the prior art are not entirely satisfactory for this recording purpose for a number of reasons. For example, it is generally true that the prior art papers which exhibit high sensitivity to an exposure of short duration to a high intensity beam tend to exhibit a correspondingly low degree of background stability. The printing out or intensification procedure for these sensitive papers is highly critical and accordingly is exceedingly difiicult if not impossible to carry out. The latent image may be entirely lost during the subsequent latensification operation due to the fact that the background comes up or prints-out too rapidly. In other cases a phenomenon known as reversal may occur, this being a darkening of the background which proceeds at a more rapid rate than darkening of the image or trace. In these situations, the trace may be temporarily or permanently lost. On the other hand, papers which exhibit a high degree of background stability tend to exhibit a correspondingly low degree of sensitivity to the recording beam and accordingly the maximum writing speed (minimum exposure time) is far below that desired for use with modern recording instruments.

Hence, when it is attempted to produce a latent image upon a low sensitivity paper at an excessive rate for the paper, the image it formed at all will become lost against the background upon print-out.

In addition to these problems, it is also critical that the sensitive paper exhibit a certain degree of permanence in order that any record prepared thereon will have a sufiiciently long and usable lifetime without losing its contrast. It is also desirable to have a sensitive paper which responds substantially uniformly to applied radiation without regard to varying intensities and different writing speeds and yet which exhibits a substantially uniform degree of contrast against the background upon latensification. According to the present invention, the sensitive films posses a sensitivity capable of writing in a wide range of speeds, including very slow speeds as well as speeds ranging up to more than 200,000 lineal inches per second. In spite of the varying requirements relative to different writing speeds, a uniform, relatively permanent and highly contrasting image is produced upon latensification. Latensification may be accomplished through exposure to radiation within the sensitive range for the paper for a very short period of time. For example, several seconds or less under an ordinary fluorescent lamp is suiticient to latensify or print-out certain images or traces made on paper prepared in accordance with the present invention.

Accordingly, it is an object of the present invention to provide improved print-out sensitive coating compo-sitions which possess both a high degree of sensitivity to a trace recording along a portion thereof together with a high degree of background stability upon general latensification.

It is a further object of the present invention to provide improved print-out sensitive coating compositions which produce an image lOr trace which has a substantially uniform degree of contrast to the background, this contrast being relatively independent of the time the sensitive material has been exposed to a relatively intense and uniform light source.

It is yet another object of the present invention to provide a print-out emulsion which produces a latent invisible image after an initial exposure time in the range of microseconds, and which will print-out the latent image upon an exposure of general application of short duration. 7

It is still a further object of the present invention to provide a photosensitive print-out sensitive coating composition which is exceedingly fast in its photographic response, which is substantially stable over a long period of time and which may be retained for an indefinite period of time so long as it is not exposed generally to light or other electromagnetic radiation for extended periods.

Other and further objects become apparent to those skilled in the art upon the study of the following specification, appended claims and accompanying drawings wherein,

FIGURE 1 is a schematic illustration of a preferred process for preparation of sensitive dispersions in accordance with the present invention; and

FIGURE 2 is a cross sectional view showing the sensitive material as a coating on a support member.

The exact theory of operation of the compositions of the present invention is not entirely understood. In silver halides generally, and in particular silver bromide, exposure to light produces elemental silver and free bromine, this phenomenon probably being carried out in accordance with the reversible equation shown below.

Applied to the present case, the free silver indicates the exposed area and a darkening of the area occurs. When the light or other electromagnetic radiation is removed, the reaction in general may tend to reverse and therefore proceed to the left with a consequent loss of indicated exposed area. Silver halide emulsions have long been employed in the photographic art, including silver bromide and silver brom-o-iodide as employed in the present invention. The presence of cadmium iodide is believed to prevent reverse reactions from occurring and hence increase sensitivity. Other halides of cadmium not within the scope of this invention, form a composition with silver halides which is less sensitive than the cadmium iodide doped material. The writing speed of compositions containing other cadmium salts is lower, and the trace, if formed, tends to fade and in some cases is substantially assimilated into the background.

By way of theoretical explanation for improvement obtained with cadmium iodide additions as applied to compositions under consideration here, it will be appreciated that precise descriptions of the mechanisms involved are difficult to set forth. It does appear however, that the cadmium iodide functions as an acceptor for the bromine liberated by light energy on the silver bromide. It is believed that this could be by Way of a displacement of the iodide ion by bromine from the silver.

Referring now to the cadmium iodide additions, the relative proportion of cadmium iodide added to the silver halide has been found to be beneficial only if held within certain limits. In cases where substantially less than about /2% of cadmium iodide by weight has been added to the silver halide sensitive mixtures, a phenomenon known as reversal has occurred. In these instances, as previously indicated, the latent image is either temporarily or permanently lost or rendered without contrast against the background upon latensification. 'If cadmium iodide is added in excess of about 20% by weight, the emulsion tends to become substantially less sensitive. Thus, in the range between /2% and 20% and in particular the range between 2% and 10% there is found to be a sound relationship between sensitivity of film and stability of background. Additions of about 5% of cadmium iodide are considered optimum.

The cadmium iodide additive as noted above, performs substantially as a bromine acceptor, and hence there is no polyvinyl alcohol are suitable.

requirement that conventional bromine acceptors such as gelatin or the like be present in the compositions of the invention.

It has been found that a small percentage of silver iodide may be added to the silver bromide. In this connection, amounts ranging from about /2% to about 5% of the co-precipitated silver iodide have been found useful, and specifically about 1% of silver iodide appears to give optimum results with respect to the mixed halides. The invention is operable using a single halide salt, e.g., AgBr, with a mechanical mixture of AgBr plus AgI, or the co -precipitated silver bromo-iodide.

The compositions of the present invention may be further sensitized if desired, by adding from .01 to .2% (by weight based on total solids) of an organic sensitizer such as thiourea which is the preferred sensitizer for this composition. Thiocarbamide, tbiosemicarbazide, paramethylamino phenol sulphate and mercapta succinic acid are useful and may be employed if desired.

Various inert carriers or binders, and particularly organic colloid carriers, may be employed in order to facilitate application and adhesion of the sensitive composition to paper in dispersion or emulsion fnom either aqueous compatible or aqueous incompatible carriers. In an aqueous system, pregelatinized dextrin, gelatin, starch, dextrin, thickening agents such as sea-weed extracts or In the nonsoluble systems, silicones may be employed. If desired, coatings without a binder may be applied in dry form e.g. by electrostatic application and subsequently covered with a suitable conventional protective film. The car-riers do not substantially affect the photographic properties of the compositions, but are merely used to adhere the composition to the base material.

Among the various base papers or supports, one may employ almost any sort of cellulose paper so long as it is free from wood chips or the like. Conventional photographic base papers may be conveniently utilized.

Heat treating the coated paper when carriers other than gelatin have been used has been found advantageous in increasing top writing speeds and retarding the rate of background rise. In this connection, heating to a temperature of about 400 'F. or greater for a period of from 10 to 30 seconds produces beneficial results, it being necessary to avoid scorching the paper. Specifically a temperature of about 400 F. for a period of about 20 seconds has been considered the optimum for compositions prepared in accordance with the present invention. Somewhat lower temperatures, in the range of from about 300 F. to 400 F. may be employed for somewhat longer periods of time. Temperatures as low as 200 F. have been found to improve the qualities of the coated paper, this improvement being somewhat less than that achieved when higher temperatures are employed. For example, one coated paper was heat treated at 200 F. for 5 minutes and tested for writing speeds. A trace written at a speed equivalent to about 200,000 inches per second was clearly visible, although the background after print-out was somewhat darker than desired. Papers treated at 400 F for about 20 seconds record well at this speed and are considered to have superior background characteristics.

For exposure and latensification, the maximum sensitivity of the paper is found to be below about 5000 angstroms, and mainly below about 4400 angstroms. Various commercially available high intensity light sources may be conveniently employed for producing the trace image, such as for example the Osram lamp manufactured by Osram, Munich, West Germany, as hereinafter identified in Example I. By the term high intensity radiation reference is made to electromagnetic radiations having an intensity of about 10 ergs/sec./cm. or greater. In order to obtain a useful trace, this radiation 'is applied to the material for a period of about 10- seconds or greater. Although lower intensity sources may be satisfactorily utilized, these sources may require substantially higher total enengics inasmuch as the material exhibits a low intensity reciprocity failure.

While the sensitive films are particularly sensitive to radiations of relatively high intensity, they are also suitable for use at lower intensities, with a corresponding drop in writing speed. For latensification, a less intense source of light available generally across the extent of the paper is desired. Ordinary fluorescent lighting at close range is useful both in its intensity and its output wave lengths characteristic for latensification operations. For example, latensification may be carried out under the influence of illumination of the order of 75 foot candles of coolwhite fluorescent light.

In order to more particularly set out the features of the present invention, specific examples of preparation are presented hereinbelow:

EXAMPLE 1 In the preferred embodiment of the present invention, the following preparation is recommended.

Preparation of Silver Nitrate Solution Compound: Amount AgNO 170 gr. (1.0 mol). H O(distilled) 1000cc.

NH (28-30% aqueous solution,

sp. \gr. 0.90) 400 cc.

The silver nitrate was weighed and dissolved in the prescribed amount of distilled water. Then the ammonia solution was added with stirring until the solution cleared as the precipitate of silver oxide formed by the first added portions of the ammonia was redissolved.

Potassium Halide Solution Compound: Amount Kl 1.66 gr. (0.0l0 mol). liBr 143 gr. (1.20 mol). H O (distilled) 300cc.

The potassium iodide was weighed carefully in order to insure precise control over the iodide content of the resultant silver halide mixture. The potassium halides were dissolved in the prescribed amount of water contained in a two-liter beaker which was set in a waterethylene glycol bath. The bath was heated on a hot plate to about 70-80 C. The solution of potassium halide was stirred mechanically with a stainless steel stirrer.

Preparation of Silver Bromo-Iodide When the halide solution was hot (70 to 80 C.) the ammonia-cal silver nitrate solution was added slowly in a steady stream to the reaction vessel. This was done by pouring the silver solution slowly into a funnel to the outlet of which has been fused a short length (about 4 inches) of capillary tubing. The capillary jet delivered the silver solution at a rate of about 30 cc. per minute, so that the addition of silver was completed in about 50 minutes. The iodide reacts preferentially because of its being less soluble than the silver bromide. In this connection, there may be considerable co-precipitation so that silver iodide is trapped in silver bromide crystals with the result that strained crystals of high sensitivity are formed.

Ammonia and potassium bromide act as solvents for the silver halides formed and promote crystal growth. Thus, in the presence of these solvents, the smaller silver halide crystals may dissolve and be re-deposited on the surfaces of larger crystals by a process known as Ostwald ripening. This process can occur during the slow precipitation step. The mixture was stirred vigorously with a mechanical stirrer during the precipitation period.

After the precipitation step, the silver halide mixture was filtered by suction on a Biichner funnel and was washed five times with distilled water. It is not normally necessary to dry the silver halides after filtering and washing.

Compounding of Print-Out Coating Mixture In addition to silver bromo-iodide, the following ingredients were utilized in preparing a preferred mixture in accordance with the present invention:

Cadmium iodide (to increase the print-out effect and to suppress background during latensification). Starch (to bind the ocating to the paper support).

Compound: Amount Silver halide (as prepared hereinabove) gr Cadmium iodide gr H O (distilled) cc 30 Starch solution (28% starch) gr 73 The ingredients listed above with the exception of the starch solution were placed in a pint porcelain jar of a ball mill containing 200 grams of one-half inch porcelain pebbles. The bottle was rotated at about 60 r.p.m. for a period of one hour. The starch was then added and the mixture ball-milled for another one hour period, after which time a homogeneous mixture resulted. The mixture described above had a consistency which was found suitable for making flow-coated papers.

In this connection various application techniques may be employed, such as transfer roller coating, dip coating using an air-knife to wipe oh the excess upon emergence from the bath, or by conventional spreading using a doctor knife to control the thickness of the film. Although the thickness of the coatings to be applied to paper or other supports is dependent on the characteristics desired in the end product, it has been found that the composition disclosed above was when applied in layers calculated to be in the range of about 0.5 mil in thickness useful. As the thickness of the wet film is diflicult to measure, it is somewhat easier to use the weight per unit area of solids deposited as a reference. About 2 grams of solids per square foot of the dried film appears to be satisfactory. The critical features are that the coating be uniform, flexible, and adherent to the base material. After application to the base paper, the coating was dried and was subjected to a temperature of about 400 F. for a period of 20 seconds.

Attention is directed to FIGURE 2 of the drawings wherein there is illustrated a photosensitive paper having a base support and a sensitive coating. This coating was prepared as in Example 1 above.

The sensitive material prepared in accordance with Example I above and shown in FIGURE 2 was yellow in color and upon the desired exposure to light, a uniform medium dark brown image or trace having extremely fine edge definition was formed. Sensitive papers prepared according to this process were capable of writing speeds equivalent to more than 200,000 inches per second when illuminated from a source having an intensity of about 100,000 candles/sq. cm. under the spectrum distribution obtainable from a high pressure mercury vapor arc lamp such as the Osram lamp manufactured by Osram, Munich, West Germany, and identified as their model HBOAOV/l High Pressure Mercury Lamp, this lamp being employed as specified in the aforementioned application of Mahoney et al. A high proportion of this radiation is in the ultraviolet. A complete system for recording is described and disclosed in the aforementioned Mahoney et al. application.

In printing out, subsequent to formation of the latent trace the entire sensitive paper was exposed to low intensity ambient light in the range of 50 to 75 foot'candles of fluorescent radiation for a few minutes. At this time, traces prepared at speeds less than about 50,000 to 70,- 000 inches per minute were prominent and clearly visible. It appears that during this period, the background was fixed, and prolonged exposure to ambient light was possible without appreciable adverse effects. After 10W intensity post exposure, the paper was exposed to strong ultraviolet radiation for some minutes. Sunlight, high pressure or low pressure mercury lamps may be used for this purpose. During this exposure, the trace darkened considerably With the background darkening only slightly. In addition, at this time, traces prepared at speeds of from 75 ,000 to 200,000 inches per second became more prominent.

EXAMPLE 2 A silver nitrate solution Was prepared in accordance with the procedures of Example 1, and a potassium halide solution was prepared as follows.

Compound: 7 Amount KB 143 gr. (1.2 mole). H O (distilled); 300 cc.

halide solution. It is substantially as sensitive as the material of Example 1.

EXAMPLE 3 Identical techniques, preparations, and compositions were followed as in Example 1, with the exception that 2% of cadmium iodide was added to the composition rather than the as added therein. The resultant material provided a good recording paper capable of recording a distinct trace at writing speeds about as fast as those in Example 1, under the identical conditions set forth therein, the background being somewhat less stable. This trace is also uniform in color and contrast upon latensification.

EXAMPLE 4 Identical techniques, preparations and compositions were followed as in Example l'above with the exception that rather than 5% of cadmium iodide was added to the composition. This resulted in a recording paper capable of recording a uniform distinct trace at /2 as fast as those in Example 1.

EXAMPLE 5 Identical techniques, preparations and compositions Were followed as in Example 1 above with the exception that 20% rather than 5% of cadmium iodide was added to the composition. This resulted in a recording paper capable of recording a weak trace at speeds /3 as fast as those of Example 1, the background being substantially more stable.

In any of the foregoing examples, if desired, the silver halides may be precipitated in cold Water or even ice water. In addition, the crystal ripening and milling processes may be dispensed with, although the character istics of the material, for the purposes of this disclosure may be aifected adversely to some extent.

It will be appreciated from the foregoing description that the present invention makes possible the production of sensitive papers capable of giving a sharp visible image at Writing speeds of up to 200,000 in./sec. The latent image becomes visible a short time after exposure to fluorescent light, and maintains good contrast against the background "for extended periods of time. Such papers find extensive use in modern recording instruments.

Other and further modifications may be employed Without departing from the spirit and scope of the present invention. It will be appreciated of course, that the fore- 8 going examples are given for purposes of illustration only and there is accordingly no intention to limit the scope of the present invention to these particular modifications.

I claim:

1. A process for the production of photographic printout compositions sensitive to high intensity radiation of short duration and including an inert colloid carrier having a photosensitive substance consisting of silver halide and cadmium iodide dispersed theretlhrough, said process comprising coprecipitating a slurry of silver halide salts where at least 95 molar percent of the silver halideis silver bromide and the balance silver iodide, Washing said precipitate, adding between about /2% to 20% by Weight of cadmium iodide to the Washed silver halide precipitate, and forming a dispersion of said silver halide and cadmium iodide in an inert colloid carrier.

2. A process for the production of photographic printout paper sensitive to high intensity radiation and substantially insensitive to relatively low intensity radiation and including a support element coated with an inert colloid carrier and having a photosensitive substance consisting of silver halide and cadmium iodide dispersed therethrough, said process comprising coprecipitating a slurry of silver halide salts where at least 95 molar percent of the silver halide is silver bromide and the balance silver iodide, Washing said precipitate, adding between about /2% and 20% by weight of cadmium iodide based on the Weight or" the silver salts in the Washed silver halide precipitate, forming a. dispersion of silver halide and cadmium iodide in an inert colloid carrier, coating a support member With a film of said dispersion, and heating said film to a temperature of from about 200 F. up to about 400 F. for a period in excess of about 10 seconds.

3. A photographic print-out composition comprising an inert carrier having dispersed therein a photosensitive substance consisting essentially of from up to 99.5% by weight of precipitated, Washed silver bromide, the balance being cadmium iodide which is added thereto, said composition being characterized in that it is particularly sensitive to high intensity radiation of less than about 4,400 angstroms and in being substantially insensitive to ambient light intensity and wave length.

4. A photographic print-out composition comprising an inert carrier having dispersed therein a photosensitive substance, said photosensitive substance consisting essentially of about 95% by weight of a precipitated, Washed silver bromide, the balance being cadmium iodide Which is added thereto, said substance being characterized in that it is particularly sensitive to high intensity radiation of less than about 4,400 angstroms and in being substantially insensitive to ambient light intensity and Wave length.

5. A photo-graphic print-out composition comprising an.

inert organic carrier having dispersed therein a photosensitive substance, said photosensitive substance consisting essentially of from between 80% and 99.5% by Weight of precipitated Washed silver halides, said halides consisting of silver bromide containing up to about 5 molar percent silver iodide; the balance being cadmium iodide which is added thereto, said substance characterized in that it is particularly sensitive to high intensity radiation of less than about 4,400 angstroms and in being substantially insensitive to ambient light intensity and wave length.

6. A photographic print-out composition consisting essentially or" from up to 98% by Weight precipitated Washed silver halides dispersed in an inert colloid carrier, said halides consisting of silver bromide containing up to 5 molar percent of silver iodide, the balance being cadmium iodide which is added thereto, said substance characterized in that it is particularly sensitive to high intensity radiation of less than about 4,400 angstroms and in being substantially insensitive to ambient light intensity and Wave length.

(References on following page) 9 10 References Cited in the file of this patent FOREIGN PATENTS UNITED STATES PATENTS 108,193 Great Britain July 26, 1917 2,126,318 Falresen et a1 Aug. 9, 1938 OTHER REFERENCES 2,816,029 Jones Dec. 10, 1957 5 Wall and Jordan: Photographic Facts and Formulas, 2,839,405 Jones June 17, 1958 pp. 188200 (only pp. 193-196 presently relied upon) 2,843,490 Jones July 15, 1958 (1947). Published by American Photographic Publishing 3,047,392 Scott July 31, 1962 Company, Boston. (Copy in Sci. Libr.) 

3. A PHOTOGRAPHIC PRINT-OUT COMPOSITION COMPRISING AN INERT CARR INERT CARRIER HAVING DISPERSED THEREIN A PHOTOSENSITIVE SUBSTANCE CONSISTING ESSENTIASLLY OF FROM 80% UP TO 99.5% BY WEIGHT OF PRECIPITATED, WASHED SILVER BROMIDE, THE BALANCE BEING CADMIUM IODIDE WHICH IS ADDED THERETO, SAID COMPOSITION BEING CHARACTERIZED IN THAT IT IS PARTICULARLY SENSITIVE TO HIGH INTENSITY RADIATION OF LESS THAN ABOUT 4,400 ANGSTROMS AND IN BEING SUBSTANTIALLY INSENSITIVE TO AMBIENT LIGHT INTENSITY AND WAVE LENGTH. 